The invention concerns a method of actuating a device for varying the valve timing of an internal combustion engine, which method can be advantageously implemented particularly in all types of camshaft adjusting devices having a hydraulically releasable start locking.
Such a method relates particularly to camshaft adjusting devices of the generic type disclosed in DE-OS 197 26 300. These devices, generally designated in the technical field as axial piston and rotary piston adjusting devices, are arranged, irrespective of their structure, on the drive-side end of a camshaft mounted in the cylinder head of the internal combustion engine while being generally configured as hydraulic adjusting drives that comprise an element fixed in driving relationship to the crankshaft of the internal combustion engine and an element rotationally fixed to the camshaft. The element fixed to the crankshaft is in power-transmitting relationship with the element fixed to the camshaft through at least one hydraulic working chamber configured within the device, each hydraulic working chamber being divided by an adjusting element within the device into a so-called. A pressure chamber and a B pressure chamber. A pivoting or fixing of the element fixed to the camshaft relative to the element fixed to the crankshaft is effected by a selective or a simultaneous pressurizing of the A and/or B pressure chamber of each hydraulic working chamber, the pressurizing of the pressure chambers being controlled by an electromagnetically actuated valve piston of a hydraulic valve whose solenoid is actuated by a microprocessor as a function of different operation parameters of the internal combustion engine. Normally, this valve piston of the hydraulic valve permits, in a non-energized or low energized state of the solenoid, a pressurization of the B pressure chamber of each hydraulic working chamber, in a high or maximum energized state of the solenoid, a pressurization of the A pressure chamber of each hydraulic working chamber, and in a central position, a holding of the pressure medium pressure in both pressure chambers of each hydraulic working chamber of the device. When the internal combustion engine has been switched off and the volume of the A pressure chamber of each hydraulic working chamber is minimized, the element fixed to the camshaft can be mechanically coupled to the element fixed to the crankshaft in a preferred basic position for starting the internal combustion engine, coupling be achieved by an additional locking element arranged on the element fixed to the camshaft or on the element fixed to the crankshaft, which locking element can be displaced by a spring element into a coupling position within a complementary reception in the element fixed to the crankshaft or in the element fixed to the camshaft. This complementary reception of the locking element is hydraulically connected to the pressure medium supply to the volume-minimized A pressure chamber of at least one hydraulic working chamber of the device, so that, upon pressurization of the volume-minimized A pressure chamber of each hydraulic working chamber during starting of the internal combustion engine, the reception of the locking element is likewise pressurized and the locking element is displaced hydraulically, against the force of its spring element, into an uncoupling position.
This shock-like pressurization of the volume-minimized A pressure chamber generally effected by a short pulse on the solenoid at maximum energization has proved to be a drawback in practice because the sudden rise of pressure in all the volume-minimized A pressure chambers causes a bracing moment to act on the locking element which leads to a jamming of the locking element in its coupling position particularly when the mean moment of drag of the camshaft acts in the same direction as the bracing moment and/or when the time for building up the bracing moment is shorter than the time for displacing the locking element into its uncoupling position. As a consequence, a relative rotation between the element fixed to the camshaft and the element fixed to the crankshaft into a defined angle given by the microprocessor is no longer possible, so that, for example, in the case of inlet-side camshaft adjusting devices there are performance deficits of the internal combustion engine, and in the case of outlet-side camshaft adjusting devices, the internal combustion engine has higher emission values.
The object of the invention is therefore to provide a method of actuating a device for varying the valve timing of an internal combustion engine, particularly a camshaft adjusting device having a hydraulically releasable start locking, which method enables a reliable prevention of a jamming of the locking element in its coupling position even when a bracing moment resulting from a pressurization and a mean moment of drag of the camshaft impede movement of the locking element in the same direction.
The invention achieves this object in a camshaft adjusting device having a hydraulically releasable start locking, said device generally comprising following features:
the device (1) is arranged on the drive-side end of a camshaft (3) mounted in the cylinder head of the internal combustion engine and generally configured as a hydraulic adjusting drive,
said device (1) comprising an element (4) fixed in driving relationship to a crankshaft of the internal combustion engine and an element (5) rotationally fixed to the camshaft (3),
the element (4) fixed to the crankshaft is in powder-transmitting relationship with the element (5) fixed to the camshaft through at least one hydraulic working chamber (6) formed within the device (1),
each hydraulic working chamber (6) of the device (1) is divided by an adjusting element (7) within the device (1) into a pressure chamber (8) and a pressure chamber (9),
a pivoting or fixing of the element (5) fixed to the camshaft relative to the element (4) fixed to the crankshaft is effected by a selective or a simultaneous pressurizing of the pressure chamber (8, 9) of each hydraulic working chamber (6),
the pressurizing of pressure chamber (8, 9) of each hydraulic working chamber (6) is regulated by an electromagnetically actuated valve piston of a hydraulic valve (10) whose solenoid (11) is actuated by a micro processor (12) as a function of different operation parameters of the internal combustion engine,
the valve piston of the hydraulic valve (10) permits, in a non-energized or low energized state of the solenoid (11), a pressurization of the pressure chamber (9), in a high or maximum energized state of the solenoid (11), a pressurization of the pressure chamber (8), and in a central position, a holding of the pressure medium pressure (P) in both pressure chambers (8, 9) of each hydraulic working chamber (6) of the device (1),
when the internal combustion engine has been switched off and the volume of the pressure chamber (8) of each hydraulic working chamber (6) has been minimized, the element (5) fixed to the camshaft can be mechanically coupled to the element (4) fixed to the crankshaft in a preferred basic position for starting the internal combustion engine,
the mechanical coupling is achieved by a locking element (13) arranged on the element (5) fixed to the camshaft or on the element (4) fixed to the crankshaft, which locking element (13) can be displaced by a spring element (14) into a coupling position within a complementary reception (15) in the element (4) fixed to the crankshaft or in the element (5) fixed to the camshaft,
the complementary reception (15) of the locking element (13) is hydraulically connected to the pressure medium supply (16) to volume-minimized pressure chamber (8) of at least one hydraulic working chamber (6) of the device (1),
upon pressurization of the volume-minimized pressure chamber (8) of each hydraulic working chamber (6) during starting of the internal combustion engine, the reception (15) of the locking element (13) is likewise pressurized and the locking element (13) is displaced hydraulically, against the force of its spring element (14), into an uncoupling position, by the fact that the solenoid of the hydraulic valve (10) operated on starting of the internal combustion engine following a regulation strategy comprising the steps
(a) energization for a defined period of time (t), through a number of high frequency cycles of high and low energization (1), or through a defined number of such cycles, so that the valve piston of the hydraulic valve (10) oscillates in a range about its central position and enables a rapid alternating pressurization of the pressure chambers (8, 9) of each hydraulic working chamber (6) of the device (1) with a pressure (P) with which the element (5) fixed to the camshaft is held in its basic position,
(b) at the end of the defined period of time (t) or the last cycle, the routine is broken off and followed by a renewed energization or a holding of the high energization (1) for a further defined period of time (t) in which the microprocessor (12) simultaneously checks whether the element (5) fixed to the camshaft has been angularly displaced relative to the element (4) fixed to the crankshaft out of its basic-position and the locking element (13) has therefore taken its uncoupling position,
(c) if the microprocessor (12) determines that the element (5) fixed to the camshaft is still in its basic position, steps (a) and (b) re repeated till the microprocessor (12) registers that the element (5) fixed to the camshaft has been angularly displaced relative to the element (4) fixed to the crankshaft out of its basic position and that the locking element (13) has therefore taken its uncoupling position,
(d) when the microprocessor (12) determines an angular displacement of the element (5) fixed to the camshaft out of its basic position, energization with a current (1) defined by the Microprocessor (12) which is of a higher intensity than that required for the central position of the valve piston of the hydraulic valve (10) and corresponds to an adjusted angular position of the element (5) fixed to the camshaft relative to the element (4) fixed to the crankshaft.
Alternatively, the invention also achieves this object in the device by the fact that the solenoid of the hydraulic valve is operated on starting of the internal combustion engine following a regulation strategy comprising the steps:
a) energization with a high current (1) in a defined period of time (t), so that, at first, only the volume-minimized pressure chamber (8) of each hydraulic pressure chamber (6) of the device (1) and, thus also, the reception (15) of the locking element (13) is pressurized with a high pressure medium pressure (PA),
b) at the end of the defined period of time (t), the Microprocessor (12) checks whether the element (5) fixed to the camshaft has been angularly displaced relative to the element (4) fixed to the crankshaft out of its basic position and that the locking element (13) has therefore taken its uncoupling position,
c) if the microprocessor (12) determines that the element (5) fixed to the camshaft is still in its basic position, the solenoid (11) is energized with a low current (1) for a further period of time (t) for a brief pressurization of the pressure chamber (9) of each hydraulic working chamber (6) with a pressure medium pressure (PB) followed by a repetition of steps a) and b) till the microprocessor (12) registers that the element (5) fixed to the camshaft has been angularly displaced relative to the element (4) fixed to the crankshaft out of its basic position and that the locking element (13) has therefore taken its uncoupling position,
d) after determination of an angular displacement of the element (5) fixed to the camshaft out of its basic position, energization with a current (1) defined by the microprocessor (12) which is of a higher intensity than that required for the central position of the valve piston of the hydraulic valve (10) and corresponds to an adjusted angular position of the element (5) fixed to the camshaft relative to the element (4) fixed to the crankshaft.
According to the first embodiment of the method of the invention, a so-called high frequency pulsed start of the device is effected in that the solenoid of the hydraulic valve is at first energized for a defined period of time through a number of high frequency cycles of high and low energization, or through a defined number of such cycles, so that the valve piston of the hydraulic valve oscillates in a range about its central position and thus enables a rapid alternating pressurization of the A and the B pressure chambers of each hydraulic working chamber of the device with a pressure medium pressure with which the element fixed to the camshaft is held in its basic position. At the end of the defined period of time or the last cycle, the said routine is broken off and this is followed by a renewed energization or a holding of the high energization for a further defined period of time in which the microprocessor simultaneously checks whether the element fixed to the camshaft has been angularly displaced relative to the element fixed to the crankshaft out of its basic position and the locking element has therefore taken its uncoupling position. If the microprocessor determines that the element fixed to the camshaft is still in its basic position, the cycles of high and low energization are repeated for the same defined period of time, or number of cycles, followed by a renewed energization or holding of the high energization till the microprocessor registers that the element fixed to the camshaft has been angularly displaced relative to the element fixed to the crankshaft out of its basic position and that the locking element has therefore taken its uncoupling position. When the microprocessor determines an angular displacement of the element fixed to the camshaft out of its basic position, the solenoid is energized with a current defined by the microprocessor which is of a higher intensity than that required for the central position of the valve piston of the hydraulic valve and corresponds to an adjusted angular position of the element fixed to the camshaft relative to the element fixed to the crankshaft.
According to an advantageous feature of this first embodiment of the method of the invention, it is further proposed to control the high and the low energization of the solenoid of the hydraulic valve preferably by a pulse width modulated voltage control of the microprocessor, so that the energization of the solenoid within one high frequency cycle is effected, once, with an electric current having an intensity between 5% above that required for the central position of the valve piston of the hydraulic valve and 95% of the maximum intensity, and, once, with an electric current having an intensity of between 5% of the maximum intensity and an intensity that is 5% lower than that required for the central position of the valve piston of the hydraulic valve. However, in place of a pulse width modulated voltage control with this setting, it is also possible to realize this with a current regulation of a known type. Within the limits of the above-defined control ranges, the share of high and low energization of the solenoid can be freely chosen in both cases to be symmetric or asymmetric and the form of the transition from high to low energization, and vice versa, to be sudden or gradual, or the like. The respective lower limits of the pulsation ranges of the valve piston of 5% above and 5% below the energization required for the central position have proved to be of advantage because they reliably prevent a sinking of the volume flow of the hydraulic pressure medium to the A and the B pressure chamber of each hydraulic working chamber below a value at which the basic position of the element fixed to the camshaft can no longer be maintained.
As a further feature of the first embodiment of the method of the invention, it is finally proposed that, if the criterion for breaking off the routine consisting of the high frequency cycles is defined in terms of time, the duration of a cycle is preferably between 4 ms and 10 ms and the period of time for all the cycles required to displace the locking element into its uncoupling position till the breaking off of the routine is limited to a range of 10 ms to 40 ms. If, in contrast, the criterion for breaking off is defined in numbers, advantageously, the number of high frequency cycles required to displace the locking element into its uncoupling position till the breaking off of the routine is limited to 2 to 8 repetitions. It has been shown in practice, that in most cases, already one routine limited in time or in number to the ranges defined above is sufficient for reliably displacing the locking element into its uncoupling position.
According to the second embodiment of the method of the invention, in contrast, a so-called low frequency pulsed start of the device is effected in that the solenoid of the hydraulic valve is at first energized with a high current in a defined period of time, so that only the volume-minimized A pressure chamber of each hydraulic pressure chamber of the device and, thus also, the reception of the locking element is pressurized with a high pressure medium pressure. At the end of this defined period of time, the microprocessor checks whether the element fixed to the camshaft has been angularly displaced relative to the element fixed to the crankshaft out of its basic position and the locking element has therefore taken its uncoupling position. If the microprocessor determines that the element fixed to the camshaft is still in its basic position, the solenoid is energized with a low current for a further period of time for a brief pressurization of the B pressure chamber of each hydraulic working chamber. This is followed by a renewed energization of the solenoid with a high current for a defined period of time till the microprocessor registers that the element fixed to the camshaft has been angularly displaced relative to the element fixed to the crankshaft out of its basic position and that the locking element has therefore taken its uncoupling position. After determination of an angular displacement of the element fixed to the camshaft out of its basic position, the solenoid is finally energized, in this embodiment, too, with a current defined by the microprocessor which is of a higher intensity than that required for the central position of the valve piston of the hydraulic valve and corresponds to an adjusted angular position of the element fixed to the camshaft relative to the element fixed to the crankshaft.
As an advantageous feature of this second embodiment of the method of the invention, too, it is proposed to control the energization of the solenoid of the hydraulic valve preferably by a pulse width modulated voltage control of the microprocessor, so that the energization of the solenoid with a high current is effected preferably between 90% and 100% of the maximum electric current, and the energization of the solenoid with a low current is effected preferably between 0% and 10% of the maximum electric current. Similar to the first embodiment of the method of the invention, this can also be alternatively achieved using a current regulation of a known type. Within the above-defined control ranges, the share of high and low energization of the solenoid can be freely chosen in both cases to be symmetric or asymmetric. The duration of high energization is preferably set between 40 ms an 80 ms while the duration of low energization is limited to a range of between 10 ms and 40 ms. The purpose of this brief low energization of the solenoid and the accompanying pressurization of the B pressure chamber of each hydraulic working chamber is to bring the element fixed to the camshaft that, due to the previous pressurization of the A pressure chamber of each hydraulic working chamber, has been rotated through an angle (up to 1xc2x0 crankshaft angle) corresponding to the operational play of movement of the locking element and that may be jamming the locking element, back into a position in which the locking element can move freely for the next releasing attempt.
Both embodiments of the method of the invention for actuating a device for varying the valve timing of an internal combustion engine, particularly a camshaft adjusting device having a hydraulically releasable start locking thus permit, in contrast to prior art actuating methods for devices of a similar type, a reliable prevention of a jamming of the locking element in its coupling position during the starting of the internal combustion engine even when a bracing moment resulting from the pressurization of the volume-minimized A pressure chamber of each hydraulic working chamber of the device and a mean moment of drag of the camshaft impede movement of the locking element in the same direction. The high and low frequency energization of the solenoid of the hydraulic valve with a high and a low current and the accompanying alternating pressurization of the A and the B pressure chamber of each hydraulic working chamber of the device causes a xe2x80x9cjoltingxe2x80x9d movement of the locking element which guarantees a reliable movement of the locking element into its uncoupling position and, thus also, a reliable releasing of the start locking of the device. In this way, already immediately after the starting of the internal combustion engine, relative rotations between the element fixed to the camshaft and the element fixed to the crankshaft into defined angular positions given by the microprocessor are possible, and negative consequences such as reduced performance or increased emission of the internal combustion engine are excluded.